A typical water heater for residential hot water production and storage is an electrical resistance water heater and storage tank, although gas water heaters are also used to heat water in a storage tank. Water heaters typically include a storage tank defining a chamber for retention of water. A water inlet pipe is provided with a first connection for interconnection with a cold water supply line that conveys fresh, relatively cold water into the storage tank. In the case of electrical resistance water heaters, there are electrical resistance elements, within the storage tank, that heat the water.
An alternative method for heating water is an active desuperheater water heater. In one example of an active desuperheater water heater, the active desuperheater water heater uses a small pump to circulate water from a water storage tank, through a heat exchanger, and back into the water storage tank. The active desuperheater water heater intercepts the superheated hot gas that is rejected from an air conditioner or heat pump compressor, sitting outside the home, and transfers the heat to the water circulating through the heat exchanger. The active desuperheater water heater works only when the air conditioner or heat pump is operating in a cooling mode.
Another alternative method for heating water is a heat pump water heater. A heat pump water heater contains a fan, compressor, and an evaporator configured to sit on top of the water storage tank. The heat pump water heater circulates a refrigerant through an evaporator and compressor, and uses a fan and evaporator to pull heat from air surrounding the heat pump water heater in order to heat the refrigerant. The heated refrigerant runs through a condenser coil within the water storage tank, transferring heat to the water stored therein.
Yet another alternative method for heating water is a HVAC system coupled with a water heater module to form a multi-purpose system. This multi-purpose system utilizes a water heater module to divert a refrigerant to an indoor unit assembly when conditioning an interior space, or to the water heater module's heat exchanger when heating water. The outdoor heat pump circulates a refrigerant through an evaporator and compressor, and uses a fan and the evaporator to pull heat from air surrounding the heat pump in order to heat the refrigerant. The heated refrigerant runs through the water heater module heat exchanger, transferring heat to water also circulating through the water heater module heat exchanger.
During interior space cooling operation, 10-15% of the system refrigerant is typically contained within the indoor unit assembly. During interior space heating operation, 50-60% of the system refrigerant is typically contained within the indoor unit assembly. During water heating mode, the amount of system refrigerant present in the indoor unit assembly is approximately the same as during the interior space cooling mode. When the system switches from interior space cooling mode to water heating mode, there will be a sufficient amount of refrigerant charge available to the water heater module. If the valves are switched from interior space heating mode to water heating mode, there will be an insufficient amount of refrigerant charge available to the water heater module. Therefore, there is a need for a method to manage the refrigerant charge to provide a sufficient amount of refrigerant charge to a water heater module for optimal performance.